Fluid prestress and cooling technique for gun barrel design

ABSTRACT

A gun barrel having a fluid layer between the barrel liner and case. The fluid is kept under a high pressure to prestress the liner. Between shots the fluid is replaced to remove the heat conducted by the liner.

Unite States ate t 1 1 1 1 3,727,513

Wicks 1 1 Apr. 17, 1973 FLUID PRESTRESS AND COOLING 335,607 2/1886 Meflord ..s9/14 A TECHNIQUE FOR GUN BARREL 667,525 2/1901 Huber ..89/14 A DESIGN 2,606,480 8/1952 Selin ..89/l4 A 2,026,528 1/1936 Green ..89/l4 A [75] Inventor: Lawrence E. Wicks, Dahlgren, Va.

OTHER PUBLICATTONS 73 Assignee: The United States of America as represented by the Secretary of the Universal Firearms Corp., GUNS & AMMO, Mar.

Navy 1969, Vol. 13, No. 3, pg. 2.

[22] Flled: July 1971 Primary Examiner-Stephen C. Bentley [Zl] Appl. No.: 163,641 Attorney-R. S. Sciascia et al.

52 US. (:1. ..s9/14 A [57] ABSTRACT [51] Int. Cl. .F41f 17/14 A gun barrel having a fluid layer between the barrel [58] Field of Search ..89/l4 R, 14 A, 16; lin r and case, The fluid is kept under a high pressure 42/76 76 A to prestress the liner. Between shots the fluid is replaced to remove the heat conducted by the liner.

[56] References Cited UNITED STATES PATENTS I 1 Claim, 2 Drawing Figures 335,606 2/1886 Mefiord ..89/14 A WATER gAT INLET PATENTEDAPR 1 71973 INVENTOR. LAWRENCE E W/CKS MW 0. 41%}.

AT TORNEY FLUID PRESTRESS AND COOLING TECHNIQUE FOR GUN BARREL DESIGN STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION Conventional prior art gun barrels employ one of three basic concepts. Monobloc is, as the name suggests, a one layer gun tube under no stress prior to firing. During firing the tube undergoes very high tensile hoop stresses which severely limit its pressure capability rendering it impractical for large caliber guns. Shrink fit and autofrettage, both prestress techniques, share the objective of initially compressing the barrel at the bore surface. Thus, during firing as much energy as possible is consumed in offsetting the initial compressive stress. This minimizes the final tensile stress which is a factor in the fatigue life of the barrel.

The mechanics of the shrink fit and autofrettage methods are well documented, as are their short comings. Both require a relatively high wall thickness to derive their optimum effect. This leads to an excessive weight which, at best, is inconvenient. In addition, the heavy wall thicknesses causes the bore to reach a high temperature long before the outer walls start to radiate heat. Heat transfer between the barrel and the surrounding areas is so poor that the barrel temperatures will rise to a point detrimental to the material if a prolonged firing program is carried out. This factor acts as a limitation in rapid fire guns. Increased temperatures also cause increased wear, a major curtailment to gun barrel life.

SUMMARY OF THE INVENTION The present invention provides a barrel consisting of four concentric sections whose dimensions are governed by the size of the gun itself. The innermost section, the liner, like the barrel liners in prior art guns, receives all the wear and may be replaced if necessary. The liners can be either rifled or smooth bore and the liner thicknesses are kept thin for purposes of weight reduction and cooling.

The second section is a fluid layer which is contained between the liner and the case (the third section). The thickness of this layer depends on the amount of fluid required to cool the liner. The amount is determined by the size of the gun and certain aspects of both the interior ballistics and the propellant. A relatively incompressible fluid such as water is required.

The case exists only to hold the fluid and, like the liner, is kept thin for the purpose of weight reduction. The fourth layer (or section), of a high strength to weight ratio composite material, is used to reduce the case thickness while maintaining the required case strength. A layer of radial filament winding is one alternative. The filaments could be of conventional materials (e.g., glass or steel).

The fluid is kept under high pressure for the purpose of prestressing the liner which otherwise would be too thin to support the firing pressures. A fluid inlet is provided at the breech with an outlet for the fluid provided at the barrel muzzle. During firing a partial or complete replacement of the fluid can be accomplished after each shot or every few shots as required by the heat input to the liner. All surfaces exposed to the cooling fluid are coated with a corrosion resistant material.

OBJECTS OF THE INVENTION An object of the present invention is the provision of a gun barrel having a significant weight reduction over conventional gun barrels of the same size.

Another object is to provide a gun barrel with a heat removal capability.

A further object of the invention is the provision of a fluid prestressed barrel.

Still another object is to provide a gun barrel with a liner having a longer life than that attainable under conventional designs.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a cutaway of a side view of the present invention.

FIG. 2 shows a cutaway of an end view of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 which illustrates a preferred embodiment of the present invention shows a breech ring 11 engaging a barrel liner 12 by way of threads 14. The breech ring 11 can be adapted to present breech mechanisms. The liner 12 like conventional prior art barrel liners, receives all the wear and may be replaced if necessary. The liner may be either rifled or smooth bore. A smooth bore reduces wear by eliminating the rotational forces and the sharp edges of the rifling. In either design, liner thicknesses are kept thin (1 inch for a 5 inch gun) for the purpose of weight savings and coolmg.

A second thread 15 on the breech ring 11 engages a case 16. The space between the liner 12 and the case 16 holds a pressurized fluid in a manner to be described more fully below. The case 16 exists only to hold the pressurized fluid 17 and, like the liner 12 is kept thin for the purpose of weight reduction. A layer of high strength to weight ratio composite material 18 is used as a trade off with case thickness to obtain the required strength. A layer of radial filament winding is one alternative. These elements could be of conventional materials (glass or steel etc.) and serve as a prestress medium and a strengthing backup for the case 16.

The thickness of the fluid layer 17 depends on the amount of fluid required to cool the liner 12. This amount is determined by the size of the gun and certain aspects of both the interior ballistics and the propellant. A relatively incompressible fluid such as water is required. All pressures mentioned herein are for Water and all weights and dimensions are for a 5 inch gun.

The fluid is kept under a high pressure (50,000 PSI for a 5 inch gun) for the purpose of prestressing the liner 12. Without this prestress, the liner 12 would be too thin to support the firing pressures (100,000 PS1 in a inch gun). Fluid under high pressure enters the barrel through an inlet 20 located adjacent the breech and is released through an outlet 21 located adjacent the muzzle.

Flow control of the high pressure fluid is achieved by a check valve (not shown) at the inlet 20 and a release valve (not shown) at the outlet 21. The check valve is used to prevent the surge of back pressure resulting from the differential expansion of the liner l2 and case 16 during firing. Such a surge amounts to 2,000 PSI in a 5 inch gun. The release valve is regulated to release at pressures no lower than those experienced during firing and seal again at the pressure required for the fluid prior to firing. A high pressure fluid source (not shown) is connected to the fluid inlet 20 and may consist of a separate pump and a compressor system or it may utilize pressures obtained in the recoil mechanism. The high pressure source will supply cooling fluid, at pressure, between shots.

The fluid layer will initially be filled at atmospheric pressure and pumped up to pressure using a pump or cartridge actuated device (not shown). Thereafter, partial or full replacement of the fluid can be accomplished after each shot or every few shots as required by the layer size (dependent on the size of the gun) and heat input (determined by the ammunition).

Located at the breech and muzzle end of the fluid layer 17 are a cooperating pair of wedge seal rings 23 and 24 which provide a seal for the fluid. The seals are of a type proven in high pressure hydraulic apparatus, and derive their sealing force from the pressure of the fluid itself-the higher the pressure the higher the force. The seal rings are held in place by retaining rings 25 when not under pressure. In order to properly seat the seals and assure a good seal prior to pressurization, the retaining rings 25 are located so that they drive the seal rings into place as the liner and case are assembled. Alternatively, any other suitable seal may be employed or the liner and case may be welded together. A muzzle ring 26 joins the liner l2 and case 16 at the muzzle end of the barrel.

All surfaces exposed to the cooling fluid are coated with Teflon or its equivalent to eliminate the corrosion problem. The need for such a coating is evident although the operation of the present system is not dependent upon its use. Any corrosion resistent material may be used as a substitute for the specified material.

Many advantages are evident from the above detailed description. However, the true significance of the novel prestress technique may be gained from the following feature by feature analysis for a 5 inch gun.

Weight:

The weight of a 5 inch gun barrel fabricated according to the present invention is 3,940 pounds a 27 percent reduction over the conventional prior art 5,400 pound barrel.

Firing Pressure:

A firing pressure of 100,000 PSI is available on a 5 inch gun with lower resulting stresses than in the conventional prior art barrel design. Lower firing pressures will maintain compression in the liner even during firing (at firing pressures of 85,000 PS1 or less in a 5 inch gun).

Prestress Technique:

High pressure fluid is a very efficient prestress technique. At radius ratios (R ,/R,,,,, less than 2.3, the water provides a more efficient prestress than shrink fit and autofrettage. In addition, as the fluid is further pressurized during firing, it offers an increased resistance to further compression. Thus a fluid gives an additional prestress during firing the only time any prestress is required. Also, with the method of the present invention, the bore surface does not have to be driven plastic as it is in autofrettage.

Fatigue Resistance:

With the design concept of the present invention, tensile stresses can be kept very low, or eliminated completely. Essentially this will give an infinite fatigue life in both the case and liner. This is particularly valuable in the liner, since cracks initiated by heat checking can not propagate in compression. Stresses in the case are tensile during firing, but the filament layer keeps them low enough to rule out fatigue.

Thermal Degradation:

Neither the case nor the composite will be exposed to heat from firing since the fluid layer will carry off all heat conducted by the liner. The liner itself will operate at substantially lower temperatures than prior art liners since the heat received at the bore surface does not have a chance to build up due to the fluids cooling effect.

Bore Surface Coatings:

The availability of a method of keeping the bore surface in compression during firing makes possible the use of high temperature coatings which frequently are brittle. Such coatings will protect the bore surface from the high burning temperatures which will be present at the surface regardless of any cooling capability.

Manufacture:

Strength requirements allow use of conventional materials in thin sections for ease of fabrication and heat treating.

Cooling Capacity:

The ability to keep the barrel cool even during continued rapid rates of firing will eliminate the limits on lengths of firing programs and rates of fire.

Obviously many modification and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than is specifically described.

What is claimed is:

1. A gun barrel assembly comprising:

a barrel liner;

a case concentrically surrounding said barrel liner and spaced therefrom;

a reinforcing layer encompassing said case and formed of a high strength to weight ratio material to provide mechanical strength;

a breech ring and a muzzle ring interconnecting the ends of said barrel liner and case to define a fluid chamber;

a substantially incompressible fluid within the fluid chamber;

fluid inlet and outlet ports formed in said case and said reinforcing layer to provide fluid communication between the fluid chamber and the exterior of the assembly whereby the application of high pressure to the incompressible fluid within the fluid chamber will prestress said barrel liner in compression to enable it to withstand greater tensile hoop stresses during firing; and

fluid seals disposed within the fluid chamber adjacent the breech and muzzle rings, each seal comprising a pair of rings wedge-shaped in radial cross- 5 section and complementary in axial configuration whereby sealing pressure increases as fluid pressure increases. 

1. A gun barrel assembly comprising: a barrel liner; a case concentrically surrounding said barrel liner and spaced therefrom; a reinforcing layer encompassing said case and formed of a high strength to weight ratio material to provide mechanical strength; a breech ring and a muzzle ring interconnecting the ends of said barrel liner and case to define a fluid chamber; a substantially incompressible fluid within the fluid chamber; fluid inlet and outlet ports formed in said case and said reinforcing layer to provide fluid communication between the fluid chamber and the exterior of the assembly whereby the application of high pressure to the incompressible fluid within the fluid chamber will prestress said barrel liner in compression to enable it to withstand greater tensile hoop stresses during firing; and fluid seals disposed within the fluid chamber adjacent the breech and muzzle rings, each seal comprising a pair of rings wedge-shaped in radial cross-section and complementary in axial configuration whereby sealing pressure increases as fluid pressure increases. 